Weight is a very important factor in many electronic device applications. For example, photovoltaic generator arrays are frequently used as power sources in aerospace and military applications where weight is at a premium. The weight of photovoltaic devices is also of significant concern in other mobile applications, and in those particular applications in which transport of massive items is difficult. Specific power is a property of photovoltaic generator devices and is expressed in the units of watts (w) per kilogram of generator weight. Conventional lightweight photovoltaic generators of the type employed in aerospace applications have a specific power rating of approximately 30-50 w/kg. Ultra lightweight photovoltaic generators which are based upon thin film semiconductor materials and which employ very lightweight substrates will exhibit specific power levels in the range of 500-1500 w/kg.
In many instances lightweight and ultra lightweight photovoltaic devices, as well as other lightweight electronic devices, are manufactured by a process which involves use of a stock starting material which is comprised of a body of electronically active material, such as a photovoltaic or other semiconductor material, disposed upon a substrate. Typically, the photovoltaic material is comprised of one or more submicron thick layers of thin film semiconductor materials including but not limited to hydrogenated group IV alloy materials, and the substrate is a relatively thick support member. One step in the fabrication of lightweight electronic devices involves etching away some, or all, of the thickness of the substrate layer so as to reduce the overall weight of the device. Such etching away is typically accomplished after the device has been subjected to a number of processing steps such as affixation of electrodes, front surface encapsulation and the like.
In order to achieve maximal weight reduction it is generally desirable to reduce the thickness of the substrate to the greatest extent possible. However, it has been found that as a practical matter it is very difficult to etch a substrate down to a thickness of less than one mil. A typical substrate material may include defects, contaminants, or regions of varying composition which result in non-uniform etching, and such features can cause the formation of pinholes, cracks, voids or the like in the etched substrate, and these defects can lead to delamination or other damage to adjacent portions of the electronically active material. This difficulty in etching substrates has placed a limitation upon the fabrication of lightweight and ultra lightweight semiconductor devices.
As will be explained in detail hereinbelow, use of the present invention overcomes problems of the prior art and allows for substrates of electronic devices to be etched to thicknesses of less than one mil thereby allowing for the manufacture of very lightweight devices.